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At least 1,063 records · Page 59

Visible emission spectra of thermographic phosphors under x-ray excitation

Thermographic phosphors have been employed for temperature sensing in challenging environments, such as on surfaces or within solid samples exposed to dynamic heating, because of the high temporal and spatial resolution that can be achieved using this approach. Typically, UV light sources are employed to induce temperature-sensitive spectral responses from the phosphors. However, it would be beneficial to explore x-rays as an alternate excitation source to facilitate simultaneous x-ray imaging of material deformation and temperature of heated samples and to reduce UV absorption within solid samples being investigated. Here, the phosphors BaMgAl 10 O 17 :Eu (BAM), Y 2 SiO 5 :Ce, YAG:Dy, La 2 O 2 S:Eu, ZnGa 2 O 4 :Mn, Mg 3 F 2 GeO 4 :Mn, Gd 2 O 2 S:Tb, and ZnO were excited using incident synchrotron x-ray radiation. These materials were chosen to include conventional thermographic phosphors as well as x-ray scintillators (with crossover between these two categories). X-ray-induced thermographic behavior was explored through the measurement of visible spectral response with varying temperature. The incident x-rays were observed to excite the same electronic energy level transitions in these phosphors as UV excitation. Similar shifts in the spectral response of BAM, Y 2 SiO 5 :Ce, YAG:Dy, La 2 O 2 S:Eu, ZnGa 2 O 4 :Mn, Mg 3 F 2 GeO 4 :Mn, and Gd 2 O 2 S:Tb were observed when compared to their response to UV excitation found in literature. Some phosphors were observed to thermally quench in the temperature ranges tested here, while the response from others did not rise above background noise levels. This may be attributed to the increased probability of non-radiative energy release from these phosphors due to the high energy of the incident x-rays. These results indicate that x-rays can serve as a viable excitation source for phosphor thermometry.

42 ENGINEERING↗

Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th

The study of the origin of heavy elements is one of the main goals of nuclear astrophysics. In this paper, we present new observational data for the heavy r-process elements gadolinium (Gd, Z= 64), dysprosium (Dy, Z= 66), and thorium (Th, Z= 90) in a sample of 276 Galactic disc stars (–1.0 < [Fe/H] < + 0.3). The stellar spectra have a high resolution of 42 000 and 75 000, and the signal-to-noise ratio higher than 100. The LTE abundances of Gd, Dy, and Th have been determined by comparing the observed and synthetic spectra for three Gd lines (149 stars), four Dy lines (152 stars), and the Th line at 4019.13 Å (170 stars). For about 70 percent of the stars in our sample, Gd and Dy are measured for the first time, and Th for 95 percent of the stars. Typical errors vary from 0.07 to 0.16 dex. This paper provides the first extended set of Th observations in the Milky Way disc. Here together with europium (Eu, Z= 63) data from our previous studies, we have compared these new observations with nucleosynthesis predictions and Galactic Chemical Evolution simulations. We confirm that [Gd/Fe] and [Dy/Fe] show the same behaviour of Eu. We study with GCE simulations the evolution of [Th/Fe] in comparison with [Eu/Fe], showing that unlike Eu, either the Th production is metallicity dependent in case of a unique source of the r-process in the Galaxy, or the frequency of the Th-rich r-process source is decreasing with the increase in [Fe/H].

79 ASTRONOMY AND ASTROPHYSICS↗

Formation of a simple cubic antiferromagnet through charge ordering in a double Dirac material

Following the topological classification of electronic phases, interest has grown in materials with unique electronic or magnetic properties driven by topology and interactions. Here, in this study, we report that the topologically nontrivial mixed valent intermetalllic EuPd 3 S 4 undergoes long-range charge ordering at 𝑇 𝐶⁢𝑂 = 340 K wherein 𝐽 = 7/2 Eu 2+ and Van Vleck 𝐽 = 0 Eu 3+ ions on a body-centered-cubic lattice separate into two interpenetrating simple cubic sublattices. The reduced symmetry transmutes 8-fold double Dirac states into 4-fold Dirac states and leads to a simple cubic Heisenberg antiferromagnet with G-type antiferromagnetic order for 𝑇 <⁢ 𝑇 𝑁 = 2.85⁢(6) K. While time reversal symmetry is broken, its combination with nearest neighbor lattice translation can form a nonsymmorphic symmetry preserving the 4-fold Dirac point. The application of a magnetic field yields a spin flop transition at the lowest temperatures but, as a consequence of the extreme isotropy of Eu, that phase transition turns into a cross-over at higher temperatures. Our work demonstrates how charge order modifies topology in EuPd 3 S 4 and exposes an archetypal simple cubic Heisenberg antiferromagnet.

Berry, Tanya [Johns Hopkins Univ., Baltimore, MD (↗

Magnetic and superconducting anisotropy in Ni-doped RbEuFe 4 As 4 single crystals

We investigate the effect of Ni doping on the Fe site in single crystals of the magnetic superconductor RbEuFe 4 As 4 for doping concentrations of up to 4%. A clear suppression in the superconducting transition temperature is observed in specific-heat, resistivity, and magnetization measurements. Upon Ni doping, the resistivity curves shift up in a parallel fashion, indicating a strong increase of the residual resistivity due to scattering by charged dopant atoms while the shape of the curve and thus the electronic structure appear largely unchanged. The observed step Delta C/T c at the superconducting transition decreases strongly for increasing Ni doping in agreement with expectations based on a model of multiband superconductivity and strong interband pairing. The upper critical field slopes are reduced upon Ni doping for in-plane as well as out-of-plane fields, leading to a small reduction in the superconducting anisotropy. The specific-heat measurements of the magnetic transition reveal the same Berezinskii-Kosterlitz-Thouless behavior close to the transition temperature T m for all doping levels. The transition temperature is essentially unchanged upon doping. The in-plane to out-of-plane anisotropy of Eu magnetism observed at small magnetic fields is unaltered as compared to the undoped compound. In conclusion, all of these observations indicate a decoupling of the Eu magnetism from superconductivity and essentially no influence of Ni doping on the Eu magnetism in this compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Spin-trap isomers in deformed, odd-odd nuclei in the light rare-earth region near $N=98$

Masses of neutron-rich, odd-odd Pm, Eu, and Tb nuclei near N = 98 were measured using the Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility. High-resolution mass measurements yielded the discovery of spin-trap isomers at N = 97 in Tb 162 , and in the N = 99 isotones of Pm 160 and Tb 164 . Furthermore, no evidence of long-lived isomers were observed at N = 95 in Eu 158 , at N = 97 in Pm 158 , nor at N = 101 in Eu 164 and Tb 166 . Here, these experimental observations are compared to results from multiquasiparticle blocking calculations.

150 ≤ A ≤ 189↗

Long-lived isomeric states and quasiparticle band structures in neutron-rich 162,164 Gd nuclei from β decay

Neutron-rich nuclei 162,164 Eu were produced by bombarding a proton beam on a 238 U target at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory and mass separating the 162,164 Eu products. New level schemes and new γ-ray transitions of the daughters 162,164 Gd were identified from β-decay spectroscopy studies. Additionally, half-lives of the 162,164 Eu were remeasured to clarify the previous ambiguous results. Two quasiparticle band structures were built and compared with neighboring nuclei. The β and γ bands were extended in 162 Gd and a γ band was extended in 164 Gd. Half-lives of the isomeric states at (6 - ) 1449 keV in 162 Gd and (4 - ) 1096 keV in 164 Gd were measured to be 99(3) μs and 0.56(3) μs, respectively. Projected shell model calculations were performed and found to be in good agreement with all of the experimental data.

150 ≤ A ≤ 189↗

Novel Valence Transition in Elemental Metal Europium around 80 GPa

We report valence transition could induce structural, insulator-metal, nonmagnetic-magnetic and superconducting transitions in rare-earth metals and compounds, while the underlying physics remains unclear due to the complex interaction of localized 4f electrons as well as their coupling with itinerant electrons. The valence transition in the elemental metal europium (Eu) still has remained as a matter of debate. Using resonant x-ray emission scattering and x-ray diffraction, we pressurize the states of 4f electrons in Eu and study its valence and structure transitions up to 160 GPa. We provide compelling evidence for a valence transition around 80 GPa, which coincides with a structural transition from a monoclinic (C2/c) to an orthorhombic phase ($Pnma$). We show that the valence transition occurs when the pressure-dependent energy gap between 4f and 5d electrons approaches the Coulomb interaction. Our discovery is critical for understanding the electrodynamics of Eu, including magnetism and high-pressure superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Values of Recovered Uranium from HALEU Used Nuclear Fuels (Rev. 1)

The value of the recovered uranium (RU) from high assay low-enriched uranium (HALEU) used nuclear fuels was evaluated. Three utilizations of the recovered uranium were considered in this study, which include the cases that RU is used as a fissile material of nuclear fuel, RU is reused in the original advanced reactor after reenrichment, and RU is reused in conventional light water reactors after down-blending. In this study, the RU values were identified by comparing the cost of making a unit mass of fuel with RU versus the fuel cost with the equivalent fresh enriched uranium (EU). A series of bounding analyses for calculating the fuel costs were conducted using several selected reactor types, which include microreactors, advanced thermal reactors, and fast reactors having a burnup of 2 – 165 GWd/t (with residual U-235 content in discharged fuels of 0.8 - 19.6%). This study concludes that RU having a residual U-235 content higher than ~7% would cost less than the fresh EU. The affordability increases as the residual U-235 content in RU increases. For instance, the fuel cost with RU having the residual U-235 content of 19.6% is about 85% cheaper than the fuel cost with the equivalent fresh EU. This study observed that reusing RU after reenrichment in the original microreactor is impractical because the U-235 content in the re-enriched RU fuel would need to be higher than the limit for low-enriched uranium (<20%) to provide the same burnup performance due to parasitic absorption from U-236. It is noted that this study focused on the recovery of uranium only, and the value of other fissile materials (such as Pu) in the used nuclear fuel was not considered even though those are bred significantly in fast reactors. In addition, the impacts of uncertainties in the cost data and the value of RU of TRISO fuels were not evaluated in this study due to the limited information on the cost data uncertainties and the separation cost from TRISO fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Phased Construction Completion Report for Decontamination Laundry Demolition at the Oak Ridge National Laboratory

This Phased Construction Completion Report (PCCR) documents completion of demolition, waste disposition, and slab stabilization activities of Building 2523 (Decontamination Laundry) for the Oak Ridge National Laboratory (ORNL). The Decontamination Laundry is located directly north of the intersection of White Oak Avenue and the 2519 Access Road. This demolition scope included the removal of the above-grade structures and facility components associated with Building 2523. This scope included the removal of Building 2523 (and all remaining contents inside), Trailer 2523A (and all remaining contents inside), an above-grade wastewater tank, and a wooden access porch connecting Buildings 2523 and Trailer 2523A. On the north side of Building 2523, above-grade portions of selected remaining foundations/stairs were removed from former Building 2517 to make room to stage waste containers. Building 2621 is west of the Laundry Building and Buildings 2547 and 2649 are to the east, while Building 2525 is to the north. Building 2523 is located within Bethel Valley Exposure Unit (EU) 3. The total area of the EU is approximately 39 acres. The area within EU 3 is bounded by First Street on the west, Central Avenue on the north, Third Street on the east and south. The slab of Building 2523 has been stabilized with a cap of flowable fill concrete and asphalt to contain residual radiological contamination and to provide surface suitable for vehicle parking. No below-grade demolition actions were performed during this task.

99 GENERAL AND MISCELLANEOUS↗

Luminescence properties of europium doped and sodium co-doped LiCaAlF 6

This paper serves as a literature review of scintillating thermal neutron detectors, along with a study of sodium and europium doped LiCaAlF 6 (LiCAF) polycrystalline material. A set of polycrystalline LiCAF material was synthesized with 2 molar percent of europium (Eu 2+ ) and co-doped with 0, 1, and 2 molar percent of sodium (Na + ), with a stoichiometric synthesis approach in a glassy-carbon crucible. The quantum yield and photoluminescence spectrum at room temperature was analyzed. For the first time, we have demonstrated that Na-co-doping directly alters the quantum yield. The quantum yield for LiCAF:Eu 2+ , with 0, 1, and 2 molar percent of sodium (Na + ) was 0.578, 0.635, and 0.580, respectively. The photoluminescence (PL) spectrum was also analyzed for all samples. The photo-luminescence excitation (PLE) spectrum showed a maximum at 300 nm, while the emission spectrum showed a maximum at 370 nm, corresponding to the Eu 2+ 5d-4f transitions.

36 MATERIALS SCIENCE↗

Impact of Glass Irradiation on Laser-Induced Breakdown Spectroscopy Data Analysis

Increased absorption of optical materials arising from exposure to ionizing radiation must be accounted for to accurately analyze laser-induced breakdown spectroscopy (LIBS) data retrieved from high-radiation environments. We evaluate this effect on two examples that mimic the diagnostics placed within novel nuclear reactor designs. The analysis is performed on LIBS data measured with 1% Xe gas in an ambient He environment and 1% Eu in a molten LiCl-KCl matrix, along with the measured optical absorption from the gamma- and neutron-irradiated low-OH fused silica and sapphire glasses. Significant changes in the number of laser shots required to reach a 3σ detection level are observed for the Eu data, increasing by two orders of magnitude after exposure to a 1.7 × 1017 n/cm2 neutron fluence. For all cases examined, the spectral dependence of absorption results in the introduction of systematic errors. Moreover, if lines from different spectral regions are used to create Boltzmann plots, this attenuation leads to statistically significant changes in the temperatures calculated from the Xe II lines and Eu II lines, lowering them from 8000 ± 610 K to 6900 ± 810 K and from 15,800 ± 400 K to 7200 ± 800 K, respectively, for exposure to the 1.7 × 1017 n/cm2 fluence. The temperature range required for a 95% confidence interval for the calculated temperature is also broadened. In the case of measuring the Xe spectrum, these effects may be mitigated using only the longer-wavelength spectral region, where radiation attenuation is relatively small, or through analysis using the iterative Saha–Boltzmann method.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Evidence from Disrupted Halo Dwarfs that r-process Enrichment via Neutron Star Mergers is Delayed by ≳500 Myr

The astrophysical origins of r-process elements remain elusive. Neutron star mergers (NSMs) and special classes of core-collapse supernovae (rCCSNe) are leading candidates. Due to these channels' distinct characteristic timescales (rCCSNe: prompt, NSMs: delayed), measuring r-process enrichment in galaxies of similar mass but differing star formation durations might prove informative. Two recently discovered disrupted dwarfs in the Milky Way's stellar halo, Kraken and Gaia-Sausage Enceladus (GSE), afford precisely this opportunity: Both have M * ≈ 10 8 M ⊙ but differing star formation durations of ≈2 Gyr and ≈3.6 Gyr. Here we present R ≈ 50,000 Magellan/MIKE spectroscopy for 31 stars from these systems, detecting the r-process element Eu in all stars. Stars from both systems have similar [Mg/H] ≈ -1, but Kraken has a median [Eu/Mg] ≈ -0.1 while GSE has an elevated [Eu/Mg] ≈ 0.2. With simple models, we argue NSM enrichment must be delayed by 500–1000 Myr to produce this difference. rCCSNe must also contribute, especially at early epochs, otherwise stars formed during the delay period would be Eu free. In this picture, rCCSNe account for ≈50% of the Eu in Kraken, ≈25% in GSE, and ≈15% in dwarfs with extended star formation durations like Sagittarius. The inferred delay time for NSM enrichment is 10×–100× longer than merger delay times from stellar population synthesis—this is not necessarily surprising because the enrichment delay includes time taken for NSM ejecta to be incorporated into subsequent generations of stars. For example, this may be due to natal kicks that result in r-enriched material deposited far from star-forming gas, which then takes ≈10 8 –10 9 yr to cool in these galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

Overview of the Long-Term Stewardship of the Remediated Uranium Mining and Milling Sites in Europe - 20079

Uranium mining in Europe began in the ' 40's for civil and military applications. The great majority of the uranium mines have now been closed and are going through the stages of decommissioning and/or rehabilitation. Today, the main uranium producers are outside the EU; only a few mines are still in operation inside the EU. In 2006, the situation of the uranium mines and mill tailings in Europe, identifying the tailings liabilities, their status, the plans for these sites and any associated hazards, was reported to the EC. The legacy of uranium mines and mill tailing disposals in the EU are located mainly in 12 Member States where, in total, 87 tailing objects were identified at 63 sites. The volume of each one of these tailings disposal varies from a few thousand to several tens of million m{sup 3}. The majority of these sites are no longer in operation. More than 40 tailing embankments have already been completely remediated. Approximately 20 are currently being remediated while for the remaining objects, remediation has yet to start. After ten years, and for a few cases where the respective projects have not yet been completed, it seems that most of Europe's uranium mines and milling legacies were remediated according to acceptable environmental standards. Nevertheless, Europe is about to face a new challenge that comes from the concluded remediation projects for which an effective set of measures for coordinated institutional control, known as 'long-term stewardship', is needed including, in most cases, continuous and active maintenance. Moreover, the uncertainty of what will happen to these sites if institutional control fails at some point in time is a major concern. This work presents a summary of the situation and current issues of the uranium mine and mill tailings in Europe and their remediation status. It addresses not only the management of existing uranium mine and mill legacies but also the methods and strategies that have been used to prevent the creation of new future legacy sites from uranium mines still in operation. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Materials Data on EuCuTeF by Materials Project

EuCuTeF is Parent of FeAs superconductors structured and crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Eu2+ is bonded in a 4-coordinate geometry to four equivalent Te2- and four equivalent F1- atoms. All Eu–Te bond lengths are 3.37 Å. All Eu–F bond lengths are 2.54 Å. Cu1+ is bonded to four equivalent Te2- atoms to form CuTe4 tetrahedra that share corners with four equivalent CuTe4 tetrahedra, corners with twelve equivalent FEu4Te4 tetrahedra, edges with two equivalent FEu4Te4 tetrahedra, and edges with four equivalent CuTe4 tetrahedra. All Cu–Te bond lengths are 2.67 Å. Te2- is bonded in a 12-coordinate geometry to four equivalent Eu2+, four equivalent Cu1+, and four equivalent F1- atoms. All Te–F bond lengths are 3.64 Å. F1- is bonded to four equivalent Eu2+ and four equivalent Te2- atoms to form FEu4Te4 tetrahedra that share corners with twelve equivalent CuTe4 tetrahedra, edges with two equivalent CuTe4 tetrahedra, edges with four equivalent FEu4Te4 tetrahedra, and faces with four equivalent FEu4Te4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on Eu3IrO7 by Materials Project

Eu3IrO7 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Eu3+ sites. In the first Eu3+ site, Eu3+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.38 Å) and four longer (2.75 Å) Eu–O bond lengths. In the second Eu3+ site, Eu3+ is bonded to seven O2- atoms to form distorted EuO7 pentagonal bipyramids that share corners with two equivalent IrO6 octahedra, corners with three equivalent EuO7 pentagonal bipyramids, edges with two equivalent IrO6 octahedra, and edges with two equivalent EuO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. There are a spread of Eu–O bond distances ranging from 2.27–2.64 Å. Ir5+ is bonded to six O2- atoms to form IrO6 octahedra that share corners with two equivalent IrO6 octahedra, corners with four equivalent EuO7 pentagonal bipyramids, and edges with four equivalent EuO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 39°. There is four shorter (1.96 Å) and two longer (2.00 Å) Ir–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Eu3+ and two equivalent Ir5+ atoms. In the second O2- site, O2- is bonded to four Eu3+ atoms to form a mixture of edge and corner-sharing OEu4 tetrahedra. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Eu3+ and one Ir5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on EuAsAu by Materials Project

EuAuAs is hexagonal omega structure-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent Au1+ and six equivalent As3- atoms to form a mixture of face and edge-sharing EuAs6Au6 cuboctahedra. All Eu–Au bond lengths are 3.32 Å. All Eu–As bond lengths are 3.32 Å. Au1+ is bonded in a 3-coordinate geometry to six equivalent Eu2+ and three equivalent As3- atoms. All Au–As bond lengths are 2.60 Å. As3- is bonded in a 3-coordinate geometry to six equivalent Eu2+ and three equivalent Au1+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on Eu2TeO2 by Materials Project

Eu2TeO2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Eu3+ is bonded in a 4-coordinate geometry to four equivalent Te2- and four equivalent O2- atoms. All Eu–Te bond lengths are 3.66 Å. All Eu–O bond lengths are 2.30 Å. Te2- is bonded in a distorted body-centered cubic geometry to eight equivalent Eu3+ atoms. O2- is bonded to four equivalent Eu3+ atoms to form a mixture of corner and edge-sharing OEu4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on EuPS3 by Materials Project

EuPS3 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. there are two inequivalent Eu2+ sites. In the first Eu2+ site, Eu2+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Eu–S bond distances ranging from 3.02–3.20 Å. In the second Eu2+ site, Eu2+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Eu–S bond distances ranging from 3.02–3.20 Å. There are two inequivalent P4+ sites. In the first P4+ site, P4+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 2.03–2.05 Å. In the second P4+ site, P4+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 2.03–2.05 Å. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to two Eu2+ and one P4+ atom. In the second S2- site, S2- is bonded in a 1-coordinate geometry to three Eu2+ and one P4+ atom. In the third S2- site, S2- is bonded in a 4-coordinate geometry to three Eu2+ and one P4+ atom. In the fourth S2- site, S2- is bonded in a 3-coordinate geometry to two Eu2+ and one P4+ atom. In the fifth S2- site, S2- is bonded in a 1-coordinate geometry to three Eu2+ and one P4+ atom. In the sixth S2- site, S2- is bonded in a 4-coordinate geometry to three Eu2+ and one P4+ atom.

36 MATERIALS SCIENCE↗